In the field of medical diagnoses, it is very often convenient to use erythrocytes to aid in the detection of either antigens or antibodies in a test fluid. The erythrocyte in this case is used as a carrier particle for an attached antigen or antibody. As is known, when an antigenic material is brought into contact with an antibody which is specific for that material, an antigen-antibody reaction takes place. In some systems, this reaction is visibly perceptible, resulting in an antigen-antibody complex which can be discerned either by the naked eye or with the aid of laboratory visual equipment. In other cases, however, while there is an antigen-antibody reaction, the reaction product is not discernible either to the naked eye or with the aid of auxiliary equipment at any convenient level. In situations such as these, it is very useful to provide a particle medium as a vehicle for either the antigen or antibody so that subsequent reaction with the complexing partner can be visualized because clumping or agglutination of the particles is effected.
The art has used a variety of particulate materials as the base upon which to attach the antigen or antibody for subsequent reaction, including latex particles such as styrene, butadiene, acrylic polymers and various blood cells such as human and animal erythrocytes (red blood cells). Erythrocytes are a very fragile, delicate component of blood, constituting the basic medium upon which antigens are carried throughout the host system. For example, human red blood cells are known to carry a wide variety of various antigens, the nature and composition of which give rise to a fingerprint which is useful in determining what kind of blood a recipient could tolerate upon a transfusion.
When red cells are used to detect antigen-antibody reaction, the resulting agglutination is termed hemagglutination, and when the red cell is used to carry an antibody rather than an antigen for detection of a suspect antigen in host serum, the phenomenon is called reverse passive hemagglutination.
As illustration of a reverse passive hemagglutination is the well-known detection system for the presence of hepatitis associated antigen in a patient's serum. The difficulty with using red blood cells in such a hemagglutination system, or indeed in any antigen-antibody detection system, is that red cells are extremely fragile, delicate and unstable.
If red blood cells are left suspended in an isotonic medium, they will lyse within about twenty-one days. That is, the supporting structure of the red blood cells will start to weaken and cause the leakage of hemoglobin into the environment. Lysis of the cell results, making the material wholly unsuitable for any use in an agglutination detection system.
The present invention is concerned with treating red blood cells to improve their stability and permit their use in antigen-antibody reaction detection systems. The process of so treating red blood cells is called fixation.